ATPL met question

[xxRED BARONxx]

Hey guys, Im about to sit atpl met and I was just going through some practice questions when I ran into this one and couldnt get my head around it...

Q: If the ambient temperature is warmer than standard at FL350, the density altitude compared to the pressure altitude is:

a) Lower than pressure altitude
b) Impossible to determine without information on possible inversion layers at lower altitudes
c) Higher than pressure altitude
d) Equal to pressure altitude

Can someone please offer an explination?

thanks in advance

[Whiskery]

It's (c) - higher than pressure altitude.

[TOUCH-AND-GO]

Pressure altitude is the altitude read from the instrument when set to a barometric setting e.g 1013.25hp. This altitude does not factor ambient temperature. Density Altitude is the Altitude where the aircarft believes it may be.

In general, the density of the atmosphere decreases as altitude rises. It also decreases as temperature increases. A high density altitude doesn't mean high density. It means the density is such that the performance of an airplane will make the airplane think it's at a higher altitude. Regardless of the actual altitude (or elevation if it's on the ground), if the temperature is higher than a standard day, the density altitude will be higher and the aircraft performance will be lower.

Hope that it explains it! Answer is C. :cool:

[aussie027]

When temps are standard, ie in the ISA, Press alt = density alt.

Defn we were given was -- Density alt is press alt corrected for non standard temp.

So given the press alt and temp you can calculate an approx density alt, In the lower levels of atmosphere from memory it was approx 120' / *C above or below standard temp at the particular press alt. :ok:

[xxRED BARONxx]

Ahhh yep that makes perfect sense thanks!!

[belly tank]

(c)......

Good luck it's one of those exams where there is not too much guessing...learn the topic and you will be fine. From memory a few yrs ago study up on TS as I had quite a few Q on them:ok: